Ceramic powders have been utilized in dentistry for artificial teeth since the eighteenth century (Alexis Duchateau and Dubois de Chemat) and for fixed restorations (crowns) since the late nineteenth century (Dr. Charles H. Land). Porcelain powder for use by dentists and dental technicians for the building-up and shaping of dental appliances such as crowns, bridges, and artificial teeth is well known (see for example U.S. Pat. No. 3,400,097). Recent advances in technology have led to widespread use of procelains fused to various metals and other substructures such as crystalline ceramics. The various techniques involved in the use of porcelains for dental restorations all make use of a liquid binder to hold porcelain particles together to allow the powder to be built and shaped to the desired tooth form. After condensing and shaping, the liquid binder is removed from the mass, usually by heat, and the porcelain mass sintered.
The most common liquid binder used in dentistry is distilled water. Some manufacturers have tried additions of glycerine, propylene glycol or alcohol. Most additives are used to slow the drying process thus increasing the working time of the mix. Daskalon et al (U.S. Pat. No. 3,880,662, issued Apr. 29, 1975 hereby incorporated by reference) addressed this problem by substitution of part or all of the distilled water with water miscible polyhydric alcohols and ethers of alcohols. The usual procedure of shaping dental porcelain, however, remained to mix the dry powder with distilled water to a thick and creamy consistency and then apply it to the substructure (usually metal) with either a brush or spatula. The water is then withdrawn by wicking which causes the powder particles to pack more closely. This condensation of particles allows the mass to be shaped by carving. Keeping the mass moist during buildup is critical, since the powder can dry out rapidly and further placement of porcelain on a dry surface does not allow the understructure to be condensed properly. Restorations baked in such a way are more subject to air entrapment and can appear blotchy and opaque.
Proper application of porcelain powders is critical in constructing dental appliances and requires great skill not only for proper condensation, but also for correct development of color. The ceramist is required to place various shaded powders in order to achieve desired gradations of color and translucency in the finished product. This must be accomplished without seeing the true shades and modifications until the porcelain mix is sintered or vitrified. This requires great skill and imagination. Some dental porcelain manufacturers have tried to facilitate this process by the addition of organic dyes to allow differentiation of the blends of the various powders during the buildup. However, these colorants are arbitrary and bear no relation to the sintered shades.